This invention relates to apparatus and a method of producing articles from thermoplastic material and, particularly, to apparatus and a method of producing chair or floor mats for supporting castered chairs or the like on a subjacent support surface or floor.
It is well known in the art that chair mats are placed on top of carpeting in offices, for instance, so that when castered furniture rolls across the surface of the mat it does so more easily than rolling across the surface of a carpeted floor. Most offices throughout the country use such chair mats with carpeted flooring, as well as to prevent marring of other types of flooring.
Many such chair mats include integral elongated projections or cleats extending transversely from the lower surface of the mat. This also is true of elongated runners of thermoplastic material, such as vinyl, used in homes as a protective overlay for expensive carpeting. The projections or cleats are provided to prevent mats or runners from sliding relative to the surface of the carpet.
Machines are known for forming plastic material into elongated webs and for defining, or embossing, by pressure, a continuous pattern in the surface of the web to a relatively shallow depth. An improvement in such machines and processes is disclosed in U.S. Pat. No. 3,430,291 to Charles F. Hlinka, dated Mar. 4, 1969, and assigned to the assignee of this invention. Hlinka shows a novel machine and process for economically producing an endless web or runner with well defined, elongated cleats thereon that extend transversely to the plane of the web. This is done by extruding a thermoplastic sheet between a pair of calendering or pressure rollers, one of which is provided with elongated, vented extrusion bores into which heated plastic of the web in molten form is forced to form the cleats. However, Hlinka forms the projections or cleats in a continous manner over substantially the entire linear dimensions of the web.
Continuous cleated webbing as produced by the Hlinka process and/or machine can be used for producing chair mats, including irregularly shaped mats which have a forward projecting tongue portion normally positionable under a desk top between the side drawer portions of the desk. The mat is cut from the continuous webbing, in the desired shape, and the projections or cleats span substantially the entire underside of the mat.
However, there have been at least two major problems with chair mats, particularly when used with carpeting having relatively thick pile. First, it is quite difficult to roll castered furniture onto and off of the edge of the mat. Second, the mat edge creates a safety hazard because individuals are prone to trip over the edge of the mat. These problems are caused because the peripheral edges of such mats are quite abrupt.
It has been proposed, and copending application Ser. No. 745,946 now U.S. Pat. No. 4,733,997, assigned to the assignee of this invention, discloses a peripheral approach ramp edge integral with the mat itself and having proven parameters which provide for easy rolling of castering furniture onto and off of the mat, while still preventing chipping or cracking of the mat. However, such a peripheral approach ramp cannot be formed with a mat having cleats on the underside thereof in the peripheral area adjacent the approach ramp.
This invention is directed to solving the aforesaid problems by providing an apparatus and method for producing a thermoplastic web with relatively elongated projections or cleats thereon to form chair mats, or the like, in predetermined sizes and with projections in discrete patterns so as not to interfere with forming the peripheral approach ramp thereabout.
Another problem is forming the approach ramp itself. Routing, trimming or similar machines are known for making cuts in workpieces or trimming the edges of workpieces to provide a finished appearance. However, many trimming machines are little more than buffing machines for smoothing the edges of the workpieces.
One area where edge trimming is required is in the field of manufacturing chair mats which, today, are most prevalently fabricated of vinyl or plastic material. The chair mats are irregularly shaped in that they normally include a front tongue portion for inserting beneath a desk between side drawer portions of the desk. The plastic mat normally is die cut to such a configuration and then the sharp edges are trimmed by buffing procedures which do not actually remove a significant amount of material from the mat edge.
The machine and method of this invention is directed to routing a considerable portion of the mat edge to form a beveled ramp about the mat to enable rollers or casters of chairs to easily ride onto and off of the chair mat. Control of the router is quite important so that the ramp edge is of a uniform width for aesthetic reasons.
Another problem in providing such a ramp edge is to control the thickness of the router cut so that the distal edge of the mat at the base of the ramp is not unduly thin to avoid chipping and cracking of the periphery of the mat. A further problem in routing vinyl or plastic material is to prevent undue pressure of the router blade against the mat edge. Too much pressure causes drag and excessive heat.
This invention solves the problems and satisfies the needs outlined above.